我正在尝试使用AJAX向PHP发送一个javascript变量（placeid）。我使用此变量来检索JSON对象。返回Javascript的JSON为NULL。我该如何解决这个问题？
function sendToPhp(placeid){
var url = "finals.php?placeid="+placeid;
var getJSONObj=function(url,callback){
var httpc = new XMLHttpRequest();
httpc.open("GET", url, true);
httpc.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
httpc.responseType='json';
httpc.onload= function(){
var status=httpc.status;
if(status==200){
//alert(httpc.response);
callback(null,httpc.response);
}
else{
callback(status,httpc.response);
}
};
httpc.send();
};
getJSONObj(url,function(err,jsonObjectReturned){
if(err!==null){
alert("something went wrong"+ err);
}
else
{
alert("success");
alert(jsonObjectReturned); // **returns NULL**
}
});
} // end of function
PHP脚本使用placeid返回JSON文件，如下所示：
if(isset($_GET['placeid']))
{
$placeid= $_GET['placeid'];
$apikey="someKeyValue";
$url="https://maps.googleapis.com/maps/api/place/details/json?placeid=".$placeid."&key=".$apikey;
$jsonPlacesObject=json_decode(htmlspecialchars(@file_get_contents($url),true),true);
echo json_encode($jsonPlacesObject); //sending json to javascript**
die();
}